Hello,
Was the variable used for the "pilot study" the main outcome measure of
interest? If so, then you must have known all the information necessary for
conducting a power study for a full blown clinical trial. That is, you must have
had some estimate of the variance and an estimate of the clinically important
difference(s). If so, why do you need a pilot study? If not, then you don't
have enough information to do a power study to begin with...well, you could use
Cohen's rather vague "small", "medium" and "large" criteria.
Warren May
David Cross/Psych Dept/TCU wrote:
> I do believe that to the extent there is a "conventional" alpha level,
> that level is .05. In the behavioral sciences, this convention is adhered
> to rather strictly, especially by journal editors and review panels!
>
> On Wed, 15 Mar 2000, Andy Avins wrote:
>
> > We proposed a pilot clinical trial that was shot down by a local review
> > committee. Lacking any other guidance, we arbitrarily chose an alpha of
> > 0.25 for doing the power calculations (reasoning that we didn't want to set
> > too stringent a standard for rejecting the null and not proceeding with a
> > more definitive trial). We were criticized for not adopting a more
> > conventional standard of alpha=0.10. I've never heard that there was any
> > convention for this sort of calculation.
> >
> > Does anyone have any thoughts or references for sample size calculations
> > for pilot studies?
> > Thanks much in advance!
> > --Andy
> > --Andy Avins, MD, MPH
> > Assistant Professor
> > Department of Medicine
> > Department of Epidemiology & Biostatistics
> > University of California, San Francisco
> > E-mail: [EMAIL PROTECTED]
> > Tel: 415-597-9196
> >
> >
> >
> >
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